Speeds and Feeds, getting an excellent surface finish in BDMS

I don't know where the "big nose is good"-rule*) comes from. But its almost always wrong. A big radius works good with a big cutting depth, but you don't have that. Try it with a 0.2 .. 0.4 mm radius.

Nick

Hi Steve, Nick is right, a large radius requires more power to work, a larger surface area means more friction. This is OK on big lumps of metal but your con-rod is not large, and will bend or flutter with your tool. A small tip radius and finer feed than radius, should help, all things being equal. Had you thought to turn your fishtail with a hand tool? Ned Ludd

Thanks guys, I'll go and apply some HSS to the grinder...

Hadn't thought of turning this by hand, the method here is turn two tapers from the centre leaving the centre over finished dimension by about 1mm, then turn the centre section parallel and "finish with files"...

And oil and abrasive papers...

We expect to hear the results, so report back. Ned Ludd

Beautiful finish using oil an abrasives, then milled 1.5mm of the wrong side aargh!!!

Will post a picture when I get chance.

Steve

Treat as a practice piece. You now know you can get it right.

But I hope the finish was OK!

Ni-you're not alone-ck

The finish was fantastic...

One trick I have adopted is if I scrap a part I do follow through to the end, "practice piece" as Gunsmith said so I know how to make the repeat. The other reason is that one complex part I threw in the scrap in disgust, whilst having a brew I suddenly realised how to recover the mistake, which worked fine, except it was bruised from being thrown in the bin!!!

Me too! Especially if doing several of the same. In the end, I do have one (or two*) ) scrap parts. In the later steps, that scrap often helps saving time for setup.

Nick